Many electrical devices have a reference circuit for generating a reference signal based on an external source for internal use. The external source is often a supply voltage. The reference signal may represent either a reference current or a reference voltage. The reference circuit is usually designed such that the reference signal has a constant level over variations in the supply voltage, over a range of temperature, and over manufacturing process variations.
In most devices, the supply voltage is sufficient such that designing the reference circuit faces little problem. However, in devices where a reduced supply voltage is preferable, generating the reference voltage using traditional designs may encounter difficulty.